Synthesis, Characterization and Corrosion Inhibition Studies of 2-Methylbenzoylthiourea Derivatives

The effect of new corrosion inhibitors, namely N-(2-methoxyphenyl)-N’-(2-methylbenzoyl) thiourea (A1). N-(3-methoxyphenyl)-N’-(2-methylbenzoyl)thiourea (A2), N-(4-methoxyphenyl)-N’-(2-methylbenzoyl)thiourea (A3) and N-(2-methylbenzoyl)-N’-phenylthiourea (A4) on mild steel in 1.0 M H₂SO₄ with variation concentrations of inhibitors: 1 × 10⁻⁵, 1 × 10⁻⁴ and 1 × 10⁻³ M was tested by using weight loss method and linear polarization resistance (LPR) technique. These compounds were characterized using elemental analyser, FTIR, ¹H and ¹³C NMR spectroscopy. Result obtained for IR showed the important bands of thiourea compound such as ν(N–H), ν(C=O), ν(C–N) and ν(C=S) which were observed around 3200, 1670, 1250 and 700 cm⁻¹. The ¹H chemical shifts for CONH and CSNH had been observed around 11 and 12 ppm respectively. For the ¹³C resonance, the signal of C=O and C=S had been observed at 180 and 206 ppm. The presence of the inhibitors significantly reduced the corrosion rate of the mild steel. The most promising inhibitors action is at 1 × 10⁻³ M and was achieved by compound A1 where the inhibition efficiency is 82.4–86.2 %. The effectiveness of the compounds was affected by the presence and absence of methoxy as the substituents in the compounds.